133. Influence of Mastitis and of Brucella abortus Infection upon the Milk Yield of Cows

Abstract

The influence of mastitis and of Br. abortus infection, separately and combined, has been observed in two tuberculosis-free herds during the years 1929–31 and 1930–4 respectively. Actual abortions in these herds were few, but many cows were affected with Streptococcus mastitis in a subclinical form. The results, comprising the examination of 180 lactations in Ayrshires and 193 in Friesians, have been considered in relation to the results of others who have investigated the influence of Br. abortus infection on the yield.When all the lactations of all cows were considered, the average reduction in yield per lactation was 954 lb. due to mastitis and 1685 lb. due to mastitis and abortion combined. Among the Ayrshires of one herd the average reduction due to mastitis was 892 lb.